The present invention relates generally to cores made of magnetic material and more particularly to transformer or inductor cores comprising legs and yokes interconnecting the legs. The invention also relates to transformers or inductors comprising such cores and a method of manufacturing such cores.
Transformer cores are constructed from ferromagnetic materials, such as iron. This material can be provided in the form of so-called transformer plate, which easily can be cut to strips or wires of constant width. These strips or wires can subsequently be put together to cores having one or more legs and interconnecting yokes.
The Swedish patent publication SE 163 797 (Wiegand) discloses a method of making transformer cores wherein three loops of magnetic material are put together to form a cage core with delta shaped yokes. However, the resulting core suffers from some disadvantages. Firstly, the mechanical stability of the core is poor, as the different loops tend to slide relatively each other. Secondly, the circular leg areas are not filled in an efficient way.
At the present time, there are wires that have better mechanical and magnetic properties than rolled or milled strips. An example thereof is disclosed in the International patent publication WO 99/28919 (Asea Brown Boweri), wherein a magnetic core assembly is made up of wires of magnetic material. However, the transition of magnetic flux between the loops via the legs is hampered by the air-gaps between the individual wires in the loops. These air-gaps can be filled with magnetic composite, for example, but the efficiency is limited.
An object of the present invention is to provide a core of magnetic material wherein the problems of prior art are eliminated or at least mitigated.
The invention is based on the realization that a transformer or inductor core can be made of loops or rings of strips or wires wherein the strips or wires from different rings are interleaved in the core legs.
With the core according to the present invention the above mentioned drawbacks of prior art are eliminated or at least mitigated. The magnetic flux path of the inventive core has been improved over prior art and the interleaving of the magnetic material also provides mechanical stability to the core.